Recently, in the field of NAND-type flash memories, attention has been focused on a laminated-type (three-dimensional) NAND-type flash memory as a device that can achieve high integration without being restricted by the limit of resolution of the lithography technology. This type of three-dimensional NAND-type flash memory includes a laminated body and a columnar semiconductor layer. In the laminated body, a plurality of conductive films and interlayer insulating films are alternately laminated on a substrate. The conductive films function as word lines and selection gate lines. The semiconductor layer is formed to pass through these laminated films. This semiconductor layer functions as a body of a memory string. Between the semiconductor layer and the conductive film, a memory gate insulating layer that includes at least a charge storage layer is formed.
In this three-dimensional NAND-type flash memory, the ON/OFF characteristics (selection characteristics) of selection transistors are important, and it is necessary to cause a flow of a sufficient cell current during selection.